Lecture 5 - Citric Acid Cycle Electron Transport System Metabolic Rate

Citric Acid Cycle (Krebs Cycle): A crucial metabolic pathway that generates high-energy electron carriers.
Electron Transport System (ETS): Utilizes high-energy electrons from NADH and FADH2 to produce ATP.
Metabolic Rate: Indicates the energy expenditure of an individual and the efficiency of energy utilization in biological processes.

Conversion of Pyruvate: Pyruvate is converted to acetyl CoA in the presence of sufficient oxygen.
Entry into the Citric Acid Cycle: Acetyl CoA, produced in the mitochondria, enters the cycle where it is involved in various metabolic reactions.

The cycle involves the capture of high-energy electrons in the form of NADH and FADH2, while also producing ATP and CO2.
Essential to memorize all steps of the citric acid cycle, excluding the specific enzymes involved and exact molecular structures of intermediates.
Acetyl CoA consists of a 2-carbon acyl unit and coenzyme A, derived from pantothenic acid.
Byproducts of the Cycle: As the cycle progresses, NADH, FADH2, and ATP are produced, while carbon dioxide is released as a waste product.

Acetyl CoA combines with oxaloacetate (4C) to initiate the cycle.
The citrate (6C) produced goes through a series of enzymatic transformations resulting in the regeneration of oxaloacetate, with various intermediates including succinate and malate involved along the way.
Energy captured in the form of NADH and FADH2 accounts for the majority of energy extracted, with only a minor portion directly producing ATP.

The ETS operates on the inner mitochondrial membrane, where high-energy electrons from NADH and FADH2 initiate a cascade of reactions.
This process utilizes oxygen and establishes a concentration gradient of H+ ions, which is crucial for ATP generation, termed oxidative phosphorylation.
Through the series of redox reactions, energy from electrons helps create a proton (H+) gradient across the mitochondrial membrane, generating potential energy for ATP synthesis.

ATP synthase facilitates the conversion of the proton gradient into ATP as H+ ions flow back into the mitochondrial matrix.
The entire electron transport chain culminates in the reduction of oxygen to form water, with electrons combining with H+ and O2 at the end of the chain.
Byproducts of this process include ATP and heat, with an estimate of 34 ATP produced from one glucose molecule via glycolysis, the citric acid cycle, and the electron transport system.

Basal Metabolic Rate (BMR) is defined as the minimum energy expenditure required to maintain basic physiological functions at rest.
Factors that influence BMR include age, gender, body composition, activity levels, diet, hormonal levels, and genetic predispositions.

Measurement techniques involve assessing O2 consumption and CO2 production, providing insight into energy utilization efficiency.
The Respiratory Quotient (RQ) measures the ratio of CO2 produced to O2 consumed, varying based on the macronutrient composition of the diet. Typical values range from 0.7 for fat metabolism to 1 for carbohydrate metabolism.

In conditions of low oxygen, cellular metabolism switches from aerobic pathways to anaerobic processes, such as converting pyruvate to lactose in the cytosol.
This conversion is catalyzed by lactate dehydrogenase, and the result is a significantly reduced ATP yield of only 2 ATP per glucose.

Elevated lactate levels result in the sensation of muscle fatigue during strenuous activity.

The body Store energy mainly as glycogen in the liver and muscles and as fat in adipose tissue, providing a compact means of energy reserves.
The dynamics of energy conversion among carbohydrates, fats, and proteins involve several metabolic pathways and regulatory mechanisms, highlighted by the interplay of enzymes and hormonal signals.
Enzymatic Control of Metabolic Pathways: Insulin and glucagon regulate pathways such as glycogenesis and glycogenolysis, adapting to energy availability and metabolic needs.

Food energy is quantified in kilocalories, with macronutrients contributing varying energy amounts: 4 kcal/g for carbohydrates and proteins, and 9 kcal/g for fats.
The complexities of energy balance in the body ensure optimal functioning and maintenance of metabolic health.